Investigating Associative Impact of Indoor Residual Spray and Insecticide Treated Nets for Minimizing Visceral Leishmaniasis Vector Population in Bihar (India)

Background: Indoor Residual Spraying (IRS) and Insecticide Treated Nets (ITNs) are important tools in the fight against insect vectors of important diseases. In spite of having operational and logistic limitation(s), IRS and ITN are still in practice as conventional tools with mixed results for controlling Phlebotomus argentipes, the vector of Visceral Leishmaniasis (VL) in the Indian subcontinent. A combination of both tools might results better for reducing VL vector densities during the attack phase of the VL elimination initiative.

Methods: A comparison-based study was designed for analyzing the field efficacy of a combination strategy of IRS+ITN (PermaNet 3.0®) versus single interventions with IRS and ITNs alone comparing with control respectively. The study was conducted at the villages of Samastipur district of Bihar (India) using aspiration and light traps techniques (i.e., AT and LTT respectively) for collecting sand fly. The numbers of all types of sand flies (male, unfed, fed and gravid female) were recorded during a period of 12 months after the intervention in the three study arms. The bioavailability of insecticide for IRS as well as ITN was also observed at the interval of 3 months with the help of cone bioassay technique established by World Health Organization (WHO).

Results: The observed highest percent-reduction of sand flies (93.59% - 100%) at the sites with combined intervention of IRS+ITN, as compared to the sites without any intervention at control (with 0% reduction) or with single control intervention either with IRS (4.29% - 86.77%) or with ITN (60.18% - 97.07%) followed by the reduction in bioavailability of insecticide in IRS (i.e., 52.38%, 58.33%, 45.45% & 50.00%) and ITN (84.44%, 82.50%, 77.78% & 83.33%) over the period of 12 months since intervention, establishes the success of IRS plus ITN as a combined approach for contaminating vector population. Also, through the house-to-house survey at the end of study period, the acceptance of combined approach for IRS plus ITN by the community was accessed to be highest i.e., 100% as compared to the single-intervention approaches for IRS (87%) and ITN (100%).

Conclusions: Study results advocate the use of the combined strategy during the attack phase of the VL elimination initiative in order to reduce or interrupt disease transmission. It may also be a valid approach during the maintenance phase in hot-spots of VL transmission.